An inverter device for converting direct current to alternating current is known in the art, wherein semiconductor switching elements, such as transistors, are switched on and off. For example, as disclosed in Japanese Patent No. 3 633 432 (corresponding to U.S. Pat. No. 6,525,950), a semiconductor device is known in the art, wherein semiconductor elements for generating three phase alternating current, positive-polarity direct current terminals, negative-polarity direct current terminals, output terminals and so on are integrally formed.
According to the above prior art, the positive-polarity direct current terminals and the negative-polarity direct current terminals are arranged in parallel to each other, so that inductance is reduced. According to such a structure, it may be possible to reduce the inductance in electric path from a direct current power source to an inverter portion. However, inductance in the inverter portion, through which larger electric current flows, is not taken into consideration. In addition, according to the above prior art, the positive-polarity terminals connected to each positive side of respective semiconductor converting elements as well as the negative-polarity terminals connected to each negative side of the semiconductor converting elements are provided in a semiconductor module device. It is, therefore, difficult to make the module device smaller in size. In addition, it is necessary to provide a control board separately from the semiconductor module device in order to input control signals. Therefore, it is a problem that a number of parts and components will be increased.